I. Technical Field
This invention relates to an annular seal member for use in a spherical exhaust pipe joint which is adapted as an exhaust gas seal member for a spherical joint for use in connecting an exhaust pipe to be connected to an engine of an automobile or a like vehicle.
II. Description of the Related Art
Exhaust gas to be exhausted from an engine of an automobile or a two-wheeled motor vehicle is processed by a catalyst, and then, is exhausted out into the air through an exhaust pipe.
In the case of an automobile, for instance, an exhaust pipe extending from an exhaust section of an engine to a muffler section provided at a rear portion of a vehicle body is fixed to a bottom portion of the vehicle body. The exhaust pipe in the fixed state is oscillated and periodically exerted with a flexure load while being subjected to an inertia force resulting from oscillations due to a torque reaction of the engine, or acceleration/deceleration exerted thereto in driving the automobile. Such a flexure load may cause fatigue or breakage of the exhaust pipe.
An exhaust pipe equipped with a movable spherical joint 100 as shown in FIG. 14 is known as a measure for solving the above drawback.
In FIG. 14, 111 denotes an annular seal member, 110 denotes an upstream exhaust pipe to be connected to an engine section (not shown), 120 denotes a downstream exhaust pipe which is opposed to the upstream exhaust pipe 110 and is connected to an muffler section (not shown), and 130 denotes a flared seal seat having a partially concave spherical surface.
A flange portion 140 is formed on an outer peripheral surface of the upstream exhaust pipe 110, except for a portion corresponding to a pipe end portion 101 for engaging with the annular seal body 111.
The flared seal seat 130 having the partially concave spherical surface is formed on a distal portion of the downstream exhaust pipe 120. The downstream exhaust pipe 120 further includes a flange portion 150 which is integrally formed with the seal seat 130.
The annular seal member 111 is fittingly seated on a cylindrical inner surface 1 at the pipe end portion 101 in a state that the flange portion 140 is abutted against an annular end surface 3 formed on a large-diameter side of the pipe end portion 101. The downstream exhaust pipe 120 is arranged in such a manner that a partially convex spherical surface 2 serving as a sliding surface of the annular seal member 111 is brought into plane contact with the partially concave spherical surface of the seal seat 130.
The upstream exhaust pipe 110 and the downstream exhaust pipe 120 are connected with each other by threadably engaging a male threaded portion of a bolt 160 extending through the flange portion 150 in a female threaded portion of the flange portion 140. The bolt 160 extends in a coil spring 170. By threadably engaging and screwing the male threaded portion and the female threaded portion, the downstream exhaust pipe 120 is urged toward the upstream exhaust pipe 110 by a spring force. The spring force allows a relative angular displacement in oscillations of the exhaust pipe, thereby suppressing fatigue and breakage of the exhaust pipe resulting from oscillations of the exhaust pipe.
An example of the seal member to be used in the spherical joint is, for instance, disclosed in Japanese Unexamined Patent Publication No. 54-76759. Japanese Unexamined Patent Publication No. 54-76759 discloses an annular seal member which comprises a compressed wire mesh and graphite filled in the wire mesh, and which has an outer peripheral surface with a partially convex spherical configuration.
In using the seal member, however, when the spherical joint is oscillated, abnormal noise may be generated. Conceivably, generation of the abnormal noise is attributable to adhesion of the graphite filled in the seal member onto the seal seat, and abrasion of the adhered graphite against the graphite filled in the seal member.
Based on the above finding, Japanese Unexamined Patent Publication No. 58-24620 discloses a seal member having an arrangement that a lubricating composition comprising a quadrivalent ethylene fluoride resin, or a copolymer of quadrivalent ethylene fluoride and sexivalent propylene fluoride is coated on a surface of the seal member produced by compression molding a heat-resistant material including expansive graphite, mica, asbestos together with a reinforcing material including a reticular substance. The lubricating composition coated on the surface of the seal member prevents the expansive graphite and the like from adhering onto the seal seat, thereby reducing friction noise.
In the above arrangement, however, if the seal member is used in a high temperature condition of e.g. 300° C. or more, the lubricating composition may be melted or decomposed. As a result, a sufficient effect of reducing the friction noise may not be obtained.
In an attempt to solve the above drawback, Japanese Patent No. 3139179 discloses a spherical zone seal body for use in a spherical exhaust pipe joint. The spherical zone seal body is a compression molded product made of a reinforcing member including a reticular substance, and a heat-resistant material including expansive graphite, and is formed with a partially convex spherical portion on an outer peripheral surface thereof. Japanese Patent No. 3139179 recites that a lubricating layer comprising boron nitride, and at least one selected from the group consisting of alumina and silica is formed on a surface of the partially convex spherical portion.
The lubricating layer recited in Japanese Patent No. 3139179 includes boron nitride as a main ingredient. The boron nitride is a lubricating material which is less likely to be melted or decomposed at a high temperature. However, the lubricating layer including boron nitride as a single constituent is inferior in its adhesion onto the surface of the partially convex spherical portion. The invention recited in Japanese Patent No. 3139179 discloses means for improving the adhesion by adding at least one selected from the group consisting of alumina and silica, in addition to the boron nitride.
Even with use of the lubricating layer made of the lubricating composition including at least one selected from the group consisting of alumina and silica, in addition to the boron nitride, however, the adhesion is insufficient. In the case where a seal body formed with the lubricating layer having such an insufficient adhesion is incorporated in a spherical joint, the lubricating layer may be exfoliated by abrasion due to a friction of the sliding surface of the seal body against the surface of the seal seat resulting from oscillations of the spherical joint. As a result, the effect of reducing friction noise lasts only for a short time.
Japanese Patent No. 3139179 also recites a seal body formed with a lubricating layer including a polytetrafluoroethylene resin, in addition to the lubricating composition comprising boron nitride, and at least one selected from the group consisting of alumina and silica in order to enhance the adhesion. The polytetrafluoroethylene resin exhibits superior lubricity owing to its low friction property, and serves as a binder of the boron nitride or a like compound.
If the seal body formed with the lubricating layer is used in a spherical exhaust pipe joint, the effect of reducing friction noise can be obtained at ambient low temperature. However, in using the seal body at ambient high temperature corresponding to a condition where the surface temperature of the partially convex spherical portion is 300 ° C. or exceeds 400 ° C., the polytetrafluoroethylene resin may be melted or decomposed, thereby losing the function as the binder. As a result, the adhesion of the lubricating layer comprising boron nitride may be degraded, thereby resulting in exfoliation of the lubricating layer.
It has been found that the friction noise that is generated when the lubricating layer is exfoliated is of a kind of noise that is generated by the friction of metals.
It has been conceived that the friction noise similar to the noise resulting from friction of metals is generated for the following reason. Specifically, exfoliation of the lubricating layer causes direct friction of the wire mesh of the seal body against the seal seat, or friction of metallic powders generated by abrasion of the wire mesh against the seal seat, which resultantly causes the friction noise.